Various systems have been proposed for water-going vessels in which one or more rotating propellers are disposed beneath the water line of the vessel for semi-submersible vessels or disposed within a portion of the hull of submersible vessels.
Typically, the propellers in submersible systems have been driven by diesel power, steam turbines or electric motors mounted within the hull of a vessel. A propeller shaft extends through the hull to the propeller mounted on the shaft outside the hull. Such systems have the disadvantages of shaft vibration and noise radiating from the shaft. Further, leaking around the shaft occurs when the seal becomes loose or worn. Alternative systems have been suggested using shaftless electric motors mounted outside of the hull with only electric power cables passing through the hull. U.S. Pat. No. 3,182,623 provides one such example of shaftless motors used to drive impellers mounted within the tail section of a submarine. A disadvantage of such system is that propulsors (electric motors and impellers) occupy almost the entire interior of the tail section. Further, traditional shaftless electric motors are either too small to effectively move a vessel or, if large enough, add significant weight to the vessel. U.S. Pat. No. 3,101,066 suggests another shaftless electric motor for propelling a submersible vessel. Again, however, the traditional motor disclosed in the U.S. Pat. No. 3,101,066 has insufficient power to drive the vessel in which it is mounted and, if the size of the conventional motor with cylindrical iron rotor and stator is increased, the size and weight of the motor become a major disadvantage.
These prior systems have failed to address the additional problems of handling the thrust imparted by the propellers in large vessels, or the problem of handling cooling and lubrication of bearings associated with a shaftless motor mounted in a submersible vessel. Further, prior systems have failed to adequately address the problems of cooling/lubricating bearings in contaminated or muddy waters. In addition, prior systems have not solved the problem of electrical noise imparted to the vessel hull by the stator of an electric motor mounted to the hull or mechanical vibration imparted by the rotor. These and other disadvantages of the prior art systems are overcome by the unique features of the propulsion system of the present invention.